Van Allen Probes Mission and Applications

Transcription

1 Van Allen Probes Mission and Applications J. Mazur and P. O Brien The Aerospace Corporation 5 September The Aerospace Corporation

2 Topics Van Allen Probes Mission Observables from the mission Electrons in the inner Van Allen belt Inner belt protons up to ~ 1 GeV Transitory 3 rd electron belts Summary K. Kirby et al., Space Sci. Rev. 179:59-125, 2013 Our aim is to highlight examples of Van Allen Probes findings with a view to satellite applications. 2

3 Van Allen Probes Mission Launched 30 August 2012 Sun-pointed spinners at 5 rpm GTO: ~600 x 30,000 km 10 inclination Orbit period ~9 hours Data are available online but I recommend talking to these POCs if you are thinking of using VAP data for applied research: Investigation ECT (Energetic particle, composition, and thermal plasma suite) RPS (Relativistic Proton Spectrometer) Species and energy range H: 1eV MeV e - : 1eV - 10 MeV POC H. Spence H: MeV J. Mazur J. Stratton et al., Space Sci. Rev. 179:29-57,

4 Topic: Inner Van Allen Belt Electrons MagEIS is designed to tease out inner belt electrons from penetrating proton background Findings just after VAP launch: No measurable flux above ~1 MeV Lower fluxes than prior observations everywhere in the inner belt 2013: MagEIS 1990: CRRES Fennell, J. F., et al. Geophysical Research Letters 42.5 (2015): Early 2013 VAP measurements led us to speculate about the uniqueness of the current state of inner belt electrons. 4

5 Injections of Electrons Into the Inner Proton Belt 2015: MagEIS Claudepierre, Seth G., et al. Journal of Geophysical Research: Space Physics (2017): More observation time and careful background rejection have revealed the hidden dynamics of the inner belt electrons Longer observation time and improved background rejection: Still showing lower intensity than CRRES Still showing a sharply-falling energy spectrum and little-to-no flux above 1 MeV even accounting for observed injections like the 2015 March shock event VAP provides accurate observations of electrons in the challenging inner belt. 5

6 Inner Belt Electrons: Any Impacts? Possible issues: spacecraft charging and total dose Observational challenges should be a clue that any impact based on deposited charge will be minor compared to the proton environment Lower intensity than outer belt electrons at all orbits means probably not much impact Net charging in the inner belt can be positive because of stopping protons as shown by VAP/ERM VAP/ERM current Intensity ratio ~1:100 ERM data courtesy of J. Goldsten Inner belt electrons that we have observed to date are unlikely to drive TID or charging concerns. 6

7 Topic: Inner Van Allen Belt Protons VAP/RPS provides the first long-duration measurements of the proton energy spectrum to ~GeV energies (at magnetic equator where intensity is maximum) Data being included in AP9 V1.5 Research example: long-term stability of the inner belt (next charts) RPS is achieving its mission of characterizing the inner belt up to ~1 GeV. 7

8 Glimpse of the Inner Belt From 50 Years Ago 2013: RPS MeV 1963: Telstar MeV Fifty year separation in measurements yet the Telstar-2 and RPS fluxes are within ~30% of each other below L=2.5 8

9 Interplanetary Shock in 2015 Changed the Inner Belt RPS MeV We ve seen a change in the outer edge of the inner belt from the Mar 17, 2015 shock, suggesting that the RPS-Telstar-2 difference above L=2.5 is probably real. 9

10 High Proton Fluence In Perspective JESD234 hard Source of high fluence Source of fluence values References Beams used for SEE screening Test standards JESD234 (2013) JESD234 soft Solar particle events Space measurements and worst-case statistics Jiggens et al. 2014; Mewaldt year Inner Van Allen belt Van Allen Probes RPS (Mazur) ECT (Spence) 30-day RPS 1-day Proton test fluences represent a year or more exposure in GTO. VAP sees a worstcase solar proton fluence about every month. 10

11 New Electron Radiation Belts NASA press release Feb 2013: Van Allen Probes Discover a New Radiation Belt revealing the existence of unexpected structures and processes within these hazardous regions of space The phenomenon is not new VAP is providing better information about these transitory belts NASA/Van Allen Probes/Goddard Space Flight Center SAMPEX >0.5 MeV VAP can better quantify the new belts in energy and pitch angle than previous missions. 11

12 New Electron Radiation Belts: Any Impacts? Potential issues: spacecraft charging and total dose Probably not too large an impact on satellites Non-equatorial orbits will see more intense electrons in transits of the outer belt to drive charging specifications Inner/outer belts dominate TID SAMPEX/LICA had surface charging anomalies from a 3 rd belt 57 out of 3,381 (1.6%) occurred in the slot Most of these occurred in Aug 2004, just one month out of a 20-year mission AE9 captures the statistics of observed events for satellite design SAMPEX 3 rd belt Anomalies from 3 rd belt Third (or fourth, or more) new electron belts won t drive satellite designs via total dose or vehicle charging unless the orbit is circular, equatorial, and stays near L=2. 12

13 Summary Van Allen Probes has been on-orbit for 5 years The scientific productivity continues with an extended science mission now in its 5 th year The applications impact so far has primarily been in the new data for the AP9/AE9/IRENE climatological models The science and engineering communities can exploit more from the mission for satellite applications 13

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15 Proton Fluence For Quantifying SEE Risk: SEE from nuclear interactions with any material in the semiconductor Application issue: what is the right proton fluence to use for SEE testing? Aim is to irradiate all sensitive volumes with high statistical confidence Not easy to answer because there isn t one value for the areal density of sensitive volumes in a device (Ladbury 2016) Trade-offs between number of parts to test, total dose, and SEE perceptivity JEDEC standard (JESD234, 2013): 1e10 (soft devices), 1e12 (hard devices) Minimum of 100 errors Impractical for rare events 15